1. Field of the Invention
The present invention relates to a peripheral rotary milling cutter comprising a substantially cylindrical holder in which are formed one or more peripheral recesses in which are respectively and releaseably mounted a corresponding number of indexable hard metal cutting inserts. Each recess furthermore provides a chip gullet space in front of each insert.
The present invention further relates to a cutting insert having an elliptical cutting edge whereby a substantially smooth milled surface can be prepared during rotary cutting or milling.
2. Description of the Related Developments
Satran U.S. Pat. No. 5,052,863 discloses a cutting insert for use in peripheral rotary milling cutters. The cutter has a cylindrical holder and a plurality of replaceable, peripherally disposed cutting inserts. Each insert is formed with at least one cutting edge defined between a cutting rake surface and a relief flank of the insert. The cutting edge is curved along a circular radius which is an approximation of a curved side of a plane which intersects a cylinder consisting of a surface of revolution of said cutting edge at an angle corresponding to the axial rake angle of the insert in the milling cutter.
The curvature of the cutting edge of the insert of Satran is represented by the following relationship: ##EQU1## wherein:
r is the radius of curvature of the cutting edge;
l is the length of a chord joining the ends of the curved cutting edge;
D is the diameter of a cylindrical envelope of the cutting edge; and
.alpha..sub.A is the axial rake angle.
The equation set forth in Satran '863 describes a curve which is circular, and only approximates an ellipse within a given chord length. The insert of the present invention is truly elliptical and has an instantaneous radius of curvature which may be defined as follows: ##EQU2## wherein:
.rho. is the instantaneous radius of curvature of the cutting edge;
X is the length of a line from and normal to the semi-minor axis of the ellipse to any point along the ellipse.
D is the diameter of the cylindrical envelope of the cutting edge, and
.theta. is the axial rake angle.
As can be seen with regard to the equation in the present application, the instantaneous radius of the curvature varies along the edge of one quadrant of an ellipse, and is not related to or dependent upon any given chord length.